1. Field of the Invention
The present invention relates to a keyboard, and more particularly to a waterproof keyboard that prevents liquid from flowing to the motherboard.
2. Description of the Related Art
A general notebook computer 10, as shown in FIG. 1, mainly comprises a display 20, a keyboard 30 and a base 40, wherein the display 20 and the base 40 are integrally connected by a hinge. The keyboard 30 is installed on the base 40 which encloses a motherboard. The motherboard has CPU and other electronic components adhered onto the surface, and is located under the keyboard 30.
The keyboard 30 comprises a plurality of keys 31, a bottom board 35 having upturning edges 37, an elastic rubber layer 33, and a circuit board layer 34 (the latter two to be described below). Said elements are assembled into a keyboard module as shown in FIGS. 2 and 3 (wire distribution not shown), and then the assembled module is installed on the base 40.
The composition of the keyboard 30 is to be further elaborated in accordance with FIGS. 4 through 8.
FIG. 4 shows a keyboard 30 wherein a sealing layer 38 detaches from (i.e., not yet adhered) a bottom board 35, on which a plurality of keys 31 are mounted. The shape of the sealing layer 38 chiefly corresponds to that of the bottom board 35. The sealing layer 38 can be made of soft or hard plastic materials. Referring to FIG. 5, a plurality of apertures 36 are formed, through techniques like pressure-punching, on the bottom board 35 of FIG. 4. During the pressure-punching process, lugs (not shown) are also formed to lock and fix an elastic rubber layer 33 and a circuit board layer 34. The bottom board 35 in FIG. 4 and the sealing layer 38 in FIG. 5 adhere together by applying glue 39 to the bottom surface edges of the bottom board 35, or to the top surface edges of the sealing layer 38, as shown in FIG. 6. The keyboard 30, to which the sealing layer 38 adheres, then needs to go through a heating process so that the glue is solidified to unite the sealing layer 38 and the bottom board 35. After the heating process, a module of the keyboard 30 as shown in FIG. 2 is formed. Referring to cross-sectional views of the keyboard in FIGS. 7 and 8, it is understood that the keyboard 30, from the top down, mainly includes the keys 31, the elastic rubber layer 33, the circuit board layer 34, the bottom board 35 and the sealing layer 38. Since composition of the keyboard 30 is a conventional art, its detailed structure is not to be elaborated herein.
A notebook computer 10 (as shown in FIG. 1), with its compact and portable features, is generally more expensive than a desktop personal computer. There are chances that the user inadvertently spills liquid, such as drinks, on the keyboard 30 when using a notebook computer. To prevent liquid from draining through the keyboard 30 and causing damage to a notebook computer, which is often of a higher price, the conventional keyboard 30 generally comprises a sealing layer 38 disposed under the bottom surface of a bottom board 35 so as to make the keyboard 30 waterproof. With the impermeable sealing layer 38 shutting apertures 36 on the bottom board 35, a further flow of the inadvertently spilled liquid is cut off. The liquid stays on the bottom board 35 and stops flowing to the underlying motherboard through the apertures 36 on the bottom board 35. As a result, it can be assured that the liquid will not damage the motherboard, and the notebook computer maintains a normal operation.
Since keys 31 need to bear the finger pressing forces from the user, the bottom board 35 that carries the keys 31 should be made of rigid and durable materials, such as metallic materials, so as to prevent the keyboard 30 from distortion. As to the sealing layer 38, it should be made from thin sheets of certain waterproof substance that does not increase the overall thickness.
However, it should be noted that glue is used for uniting the sealing layer 38 and the bottom surface of the bottom board 35, with each of them having a size of at least 10 cm×27 cm. Since the substances of the sealing layer 38 and of the bottom board 35 have different thermal expansion coefficients, distortion resulting from thermal expansion may occur after the heating process, as shown in FIG. 9 (cf. FIG. 7 where the bottom of the keyboard remains a horizontal flat plate). The thermal expansion causes both ends of the keyboard 30 to elevate a bit and generates a cleft, which is of difference D in height, between the bottom board 35 and the horizontal line 32. That is to say, the sealing layer and the bottom board 35 cannot unite completely. Once too much liquid is spilled over and flows to the keyboard 30, the liquid may not be drained away but stay in the cleft between the sealing layer 38 and the bottom board 35, or the liquid may flow along the cleft to the motherboard underneath, causing damage that hinders the motherboard from normal operation.
In short, the bottom board and the sealing layer use two different substances that have different thermal expansion coefficients, and thus, distortion of the keyboard may occur after the heating process. The distortion prevents the sealing layer and the bottom board from uniting completely, allows liquid to flow to the motherboard under the keyboard, and causes damage that hinders the motherboard from normal operation. It is, therefore, necessary for the related industry to solve this technical problem.